1. Field of the Invention
This invention relates in general to magnetic recording and more particularly to improved apparatus for providing tracking control during the playback of recorded signal information.
2. Description Relative to the Prior Art
There is a trend toward the packing of greater and greater amounts of data on magnetic storage devices such as floppy magnetic discs and magnetic tape. Implicit in such trend is the requirement that data tracks on such recording devices be narrower and narrower, and more closely packed together In the recently announced 3.3 megabyte floppy disc, for example, the recording tracks thereof are 0.0047" wide, and on a 0.0052" pitch (guardband between tracks of 0.0005") Similarly, with a high-track-density multitrack magnetic head, say of a type that provides 400 tracks per inch, tracks would be 0.0020" given guardbands of 0.0005". It is clearly of concern, therefore, that during playback of recorded information, the information so recovered be from the correct track, and not from a neighboring one.
It is known in the art to record tracking control signals in a magnetic recording medium as a vehicle for preventing head-to-medium wander during playback of information recorded in the medium. Representative prior art in this connection may be found in U.S. Pat. No 3,474,432 which depicts the use of various prerecorded frequencies in respective tracks, the signals being mixed in such a way as to cause head position error signals to be generated in response to head-to-medium wander. Similarly, more recently issued U.S. Pat. No. 4,258 398 calls for the use of paired pre-recorded tracks as signal-sources for head orienting/positioning in connection with a multitrack configuration. Other and varied tracking control techniques have been demonstrated and taught in the art, albeit that such techniques are universally wasteful of medium (relatively wide tracking-control tracks), exhibit less than optimally tight-control and, if narrowed, are wanting when it comes to the matter of sensitivity.
A characteristic which is peculiarly common to prior art tracking-control techniques such as those mentioned above is that such techniques are dependent on flux rate-of-change while reading a control track. Attendantly, such techniques are virtually useless at low playback speeds and/or when the recorded control track signal is of too short a wavelength as to be readable during playback of the control track.